1. Field of the Invention
The present invention relates to a mobile radio communications device, and related method of operation and, in particular, to a mobile phone and related method of operation.
2. Description of the Related Arts
Mobile phones comprise a master clock circuit, i.e., an oscillator, for generating a relatively high frequency clock signal which forms part of the timebase circuitry within the mobile phone. The timebase generated within the mobile phone is intended to be synchronized with a timebase of a base station with which the mobile phone communicates in accordance with a particular communication system such as, for example; the Global System for Mobile Communication (GSM). Such synchronization is usually achieved by use of an automatic frequency control (AFC) mechanism which operates by comparing the frequency of certain signals received from the base station with the frequency of the local clock and then adjusting the local clock, i.e., the oscillator, to remove the observed frequency difference.
A plurality of mobile communication systems available have been developed which require different master clocks and timebases for their operation.
A mobile phone offering access to two or more such systems would therefore be advantageous since the same mobile phone handset could then be used with a selected one of the different communications systems supported. This choice of system for the same mobile phone would therefore lead to a greater geographical coverage for one and the same mobile phone since different communications systems commonly exhibit different geographical boundaries. This geographical limit commonly occurs at international boundaries and also occurs as a consequence of the time taken to achieve full coverage of a new network technology. Such a dual mode mobile phone would therefore be particularly attractive to users who travel overseas and also to the early users of new technology communications systems.
In order to achieve such interoperability between two respective communications systems, a mobile phone will require at least two master clock circuits serving to track the timebases and air interfaces of the respective communications systems. In order to be practically viable, such dual-mode interoperability should allow for ready switching from one communications system to the other and, in particular, allow for the calibrating of the at least two master clock frequencies with respect to each other so as to allow for an accurate and quick transition between the two communications systems.